The goal of this cross-sectional study is to evaluate whether selected serum factors are associated with the severity of diabetic retinopathy. The serum factors to be assessed include cell adhesion molecules, chemokines, and vascular endothelial growth factor. The patients will be examined only once. Data from this study may provide support for future studies in which patients are followed for the predictive values of the serum factors for the development of more severe retinopathy. The serum levels of the following factors will be determined: vascular endothelial growth factor (VEGF), sICAM-1, sVCAM-1, IL-8, MCP-1, and MIP-1 alpha. The study parameters will be the correlation of these different factors to the more severely ischemic stage of retinopathy (severe nonproliferative diabetic retinopathy and proliferative diabetic retinopathy). The role of glucose control in the pathogenesis of diabetic retinopathy is important. Hemoglobin A1C will be measured. Serum lipids may also play a role in the progression of diabetic retinopathy. Data from both the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR) and from the Early Treatment Diabetic Retinopathy Study (ETDRS) showed that elevated serum cholesterol level is associated with increased risk of retinal hard exudate. In addition, the ETDRS data showed that elevated serum cholesterol level is associated with a 2-fold increase in the risk of having retinal hard exudate and having moderate visual loss at 5 years. Patients with elevated serum triglycerides were also more likely to progress. Determinations of serum cholesterol and triglycerides will be performed. A publication has been accepted by Investigative Ophthalmology and Visual Science (IOVS).